Digital cellular systems, such as Code Division Multiple Access (CDMA) and Universal Mobile Telephony System (UMTS) systems, are currently used for providing telecommunications to stationary and mobile end user equipments. The mobile end user equipments may be mobile stations, for example mobile telephones and mobile computing devices. Such digital cellular systems divide a geographical area to be covered by the communication system into a plurality of cell areas. Within each cell is positioned a base station with which a plurality of end user equipments located within the cell communicate.
In general it is desired to have as few base stations as possible, as they are expensive, require extensive effort in obtaining planning permission and in some areas suitable base station sites may not be available. In order to have as few base stations as possible, each base station should ideally have as large a capacity as possible in order to service as large a number of end user equipments as possible.
One method of achieving an increase in capacity in a CDMA system is described in US patent application 2002/0072393 of McGowan et al. This involves the replacement of a sector wide beam width antenna with an antenna array that allows the formation of a number of narrower beams that cover the area of the original wide beam. The signal for a particular mobile station can then be sent and received only over the beam or beams that are useful for that mobile station. Such multiple narrow beams can be used for traffic channels, whereas overhead channels can be transmitted over the sector wide beam so that the overhead channels, including a pilot channel, are common to all the narrow beams in the sector. McGowan et al provides an antenna array for providing fixed narrow beams for transmitting and receiving traffic channels and for broadcasting common overhead channels over the sector using the same antenna array. This is achieved by providing appropriate frequency or phase offsets between the multiple fixed beams.
Significant optimisation of the system taught in McGowan et al is required for it to be deployed in evolving third generation (3G) communications systems, such as 1xEV-DV (1xEVolution for Data and Voice), 1xEV-DO (1x EVolution for Data Only) and HSDPA (High Speed Data Packet Access an extension to UMTS (Universal Mobile Telephony System). Also, there is a further need to increase base station capacity.